The present invention relates to a rotary drill bit comprising a cutter bit having a plurality of rows of cutting means. These rows extend along the circumference of the cutter bit and are mutually displaced generally in the axial direction of the cutter bit. The cutter bit is rotatably carried by a bit body over a bearing system, and is generally conical with an included cone angle larger than 90.degree.. The invention further relates to the use of such a drill bit as centric member in a larger unit or as an independently working unit.
Drill bits of this prior art type are disclosed in for instance U.S. Pat. Nos. 1,238,757, 2,336,335, 2,598,518 and 4,154,312. However, these previously known drill bits have been commercially used to only a limited extent due to their comparatively low drilling rate.
One object of the invention is therefore to provide a rotary drill bit of this type which has a drilling rate larger than that of hitherto known drill bits.
Boring heads having a plurality of roller cutters wherein the centric member is a one-sidedly carried conical roller cutter are disclosed in for instance U.S. Pat. No. 3,385,385 and DE-A No. 3131201. Due to the high axial feeding forces applied on such boring heads during drilling it has been found that these centric roller cutters have an unsatisfactory life.
Another object of the invention is therefore to provide a rotary drill bit of the type in question which allows use of high feeding forces while maintaining a satisfactory life.
A further object of the invention is to provide a rotary drill bit wherein the cutter bit is easily detachable from its supporting device.